Woodland scenics water effects. Paint up the bases first, attach minis (painted separately) and do your matt varnish to seal on any flock, etc, and more importantly the paint. Then do the water - the water effects is quite sticky stuff, if you attempt to flock / static grass afterwards it'll get stuck in there. Apply it with a cocktail stick to your painted (and dried and sealed) pool surface. The varnish will prevent the water effects from leeching a lot of pigment from the paint.
Note by all accounts the
WS Water Effects is different to the
GW stuff - the
WS stuff is thick, like PVA glue, but dries rubbery and clear. It's easy to put ripples and waves in it.
Good example on this scout:
This shot shows a splishy bit of the water effects:
The splashes are done by teasing the water effects as it begins to set to make contact with another dollop of it applied to the bottom of the foot. Takes a bit of practice, but works pretty well.